During a collegiate rugby season, players practice and compete for 1-2 hours on multiple days per week for 3-4 months per year. Practices and matches consist of multiple activities (e.g. sprinting, hitting, etc.) that could result in accumulated damage and affect performance. β-Hydroxy β-Methylbutyrate (HMB) is thought to speed protein synthesis which in turn could maintain performance. PURPOSE: To determine the effect of HMB supplementation on sprint kinetics throughout a rugby season. METHODS: In this cross-over design investigation, 13 collegiate male rugby players were assigned to consume one of two supplementation regimens: 5 g HMB + 5 g creatine per day (HMB) or 5 g creatine + 5 g placebo per day (PLB) for six weeks. During the fall season, players were matched for lean body mass and randomly assigned to HMB (n = 7; 21.1 ± 1.1 y; 88.2 ± 16.5 kg; 176.3 ± 7.9 cm) or PLB (n = 6; 21.5 ± 2.4 y; 88.8 ± 15.4 kg; 179.3 ± 5.2 cm). The supplementation regimen was switched for athletes who returned and completed the spring season (n = 7; 22.5 ± 1.3 y; 96.4 ± 14.7 kg; 179.6 ± 4.5 cm). Prior to and following each supplementation period (i.e., fall or spring), 40-m sprinting kinetics were assessed in all athletes while tethered to a robotic sprinting device. Peak (PK) and mean sprinting power (P), force (F), and velocity were assessed against minimal (1 kg) and heavy (15 kg) resistance. Since only 7 of the original 13 athletes returned and completed the spring season, separate 2 × 2 repeated measures analyses of variance (RMANOVA) with Bonferroni adjustments were used to assess group differences in each variable during the fall, while a 2 × 4 RMANOVA was used to assess the cross-over sub-sample throughout the fall and spring. RESULTS: While no group differences were observed in sprint kinetics during the fall, a significant group × time interaction was observed for PPK at 1kg (F = 4.85, p = 0.020, np2 = 0.55) across the fall and spring seasons, where during the spring, PPK at 1kg decreased for PLBSPRING (-6.9 ± 1.2%, p = 0.020) but not for HMBSPRING (+7.5 ± 10.7%). No other differences were observed. CONCLUSION: Our data suggest a potential benefit from HMB supplementation for maintaining sprinting power in rugby players.